Chapter 7. Linux Containers with Docker Format
/var/lib/dockerdirectory is located on a volume using the B-tree file system (Btrfs).
7.1. Components of Docker Containers
- Container – an application sandbox. Each container is based on an image that holds necessary configuration data. When you launch a container from an image, a writable layer is added on top of this image. Every time you commit a container (using the
docker commitcommand), a new image layer is added to store your changes.
- Image – a static snapshot of the containers' configuration. Image is a read-only layer that is never modified, all changes are made in top-most writable layer, and can be saved only by creating a new image. Each image depends on one or more parent images.
- Platform Image – an image that has no parent. Platform images define the runtime environment, packages and utilities necessary for containerized application to run. The platform image is read-only, so any changes are reflected in the copied images stacked on top of it. See an example of such stacking in Figure 7.1, “Image Layering Using Docker Format”.
- Registry – a repository of images. Registries are public or private repositories that contain images available for download. Some registries allow users to upload images to make them available to others.
- Dockerfile – a configuration file with build instructions for Docker images. Dockerfiles provide a way to automate, reuse, and share build procedures.
Figure 7.1. Image Layering Using Docker Format